Researchers at the University of Michigan's Law School have done something unprecedented: over the weekend, they released the country's first register of wrongful convictions. The main lesson from this wealth of data, however, is that there's much we still don't know about how many innocent people are currently in prison and why they're there.

Culling data from news reports, innocence projects, lawyers, and academics, the report looked at the country's 873 known exonerations since 1989. "If that were the extent of the problem, we would be encouraged by these numbers," researchers wrote. "But it’s not. These cases merely point to a much larger number of tragedies that we do not know about."

The register lists 79 exonerations from California and 23 from Los Angeles County, the third highest of any county in the nation. That number doesn't include "group exonerations," like the 100-150 cases dismissed after the Rampart scandal. Most of those cases involved drugs and firearms—lesser charges than found in most exoneration cases.

The registry found 83 percent of exonerations were in rape and homicide cases. Amongst the myriad causes for convicting the innocent are prosecutorial or police misconduct, false confessions and, more than anything else, eyewitness misindentification. In 64 percent of the examined exonerations, faulty eyewitness recollections played a role.